Light interference film and lamp

Abstract

An automotive lamp comprises a glass bulb having a filament and a light interference film formed on the surface of the glass bulb. The light interference film has a high-refractive index layer and a low-refractive index layer alternately stacked on each other. Each layer has a refractive index ni and a thickness di, wherein i is equal to 1, 2, . . . k. In this case, nidi is equal to (1±0.025)n 2 d 2 , wherein i is equal to 3˜(k-1), n 1 d 1 is equal to (1±0.025)n 2 d 2 , and n k d k is equal to (1±0.025)n 2 d 2 . The maximum value of the reflectance of the film is more than 91% within visible light range, and the 50% transmitting wavelength is from 515 nm to 542 nm.

What is claimed is: 
     
       1. A lamp comprising: a glass bulb having a filament therein;   a light interference film formed on the surface of the glass bulb, the light interference film including a high-refractive index layer and a low-refractive index layer alternately stacked on each other and having a maximum value of a reflectance and a 50% transmittance wavelength;   each layer having a refractive index n i  and a thickness d i , wherein i is equal to 1, 2, . . . k;   n i  d i  being equal to (1±0.025)n 2  d 2 , when i is equal to 3˜(k-1);   n 1  d 1  being equal to (1±0.025)n 2  d 2  /2; and   n k  d k  being equal to (1±0.025)n 2  d 2  /2;   the maximum value of reflectance of the film being more than 91% within the visible light range; and   the 50% transmittance wavelength being from 515 nm to 542 nm.   
     
     
       2. A lamp as set forth in claim 1, wherein a first layer of the film is a high-refractive index layer.